Polymeric sulfur (often referred to as “insoluble sulfur” because of its extremely low solubility in carbon disulfide as compared to cyclooctasulfur) and routes for its synthesis from sulfur-containing moieties have been described in the literature. For example, polymeric sulfur, also referred to herein as polymer, is known to be present in thermally equilibrated sulfur allotrope mixtures in concentrations dependent on the equilibration temperature, ranging from about 0.30 wt % or less at a temperature less than about 140° C. to a maximum of about 40 wt % between 200 and 300° C. (see Steudel, R.; Strauss, R.; Koch, L., “Quantitative HPLC Analysis and Thermodynamics of Sulfur Melts”, Angew. Chem. Int. Ed. Engl., 24(1), 1985, pp. 59-60).
Numerous US patents describe methods for polymer synthesis (see for example Belchetz, U.S. Pat. No. 2,419,309; Belchetz, U.S. Pat. No. 2,419,310; Schallis, U.S. Pat. No. 2,513,524; and Ross et al, U.S. Pat. No. 2,534,063). All involve vaporizing sulfur at high temperatures (generally above about 400° C., forming an equilibrium mixture comprising 20-40 wt % polymeric sulfur, cyclooctasulfur, and other cyclic sulfur allotropes, and then rapidly quenching the equilibrium mixture in a solvent, such as carbon disulfide, at low temperature (generally less than 60° C.) to produce a crude polymer-containing-mixture. The polymer-containing mixture is then typically extracted with solvent, for example carbon disulfide, to remove soluble sulfur impurities, for example cyclooctasulfur. After quenching and extraction the polymeric sulfur is initially amorphous but tends to convert to a microcrystalline form with residence in the solvent.
Prior art methods for manufacturing polymer all suffer from one or more drawbacks such as low per pass yields, multiple convoluted manufacturing steps requiring the use of dangerous solvents (such as carbon disulfide), and have very high energy usage because of high temperatures needed for thermal polymer formation and the rapid low temperature quench needed to preserve polymer formation. A continuing need therefore exists for a low energy, high-yield, safe, and cost-effective method for the manufacture of cyclic sulfur allotropes that meets industrial criteria for commercial implementation.